Description:Mammillaria sheldonii is undoubtedly a variable species, which has given rise to several names now ascribed to synonymy. Mammillaria alamensis is nothing else than a variant recognisable for the absence of central spines, fewer radial spines (as low as 9) and larger flowers with distinctive orange stigma lobes. The otherwise identical Mammillaria pseudoalamensis instead has green stigma lobes. Habit: It makes a cluster of basal stems.Stem: Spherical to slender-cylindrical, dull green, often becoming reddish, 3-4 cm wide, 4-8 cm tall (or more in cultivation)Tubercles: Cylindrical four-sided basally, carinate, without latex, axils without wool but with an occasional few bristles. Tubercle arrangement 8-13.Radial spines:M. alamensis usually has fewer radial spines than Mammillaria sheldonii (as low as 9), white, tipped brown, needle-like, about 6 mm long.Central spines: Absent or occasionally one in Mammillaraia alamensis and Mammillaraia pseudoalamensis ( 1 to 4 in M. sheldonii), if present elongated and either straight or hooked, about 9 mm long long, brownish, the upper part dark blackish brown.Flowers: Large up to 3,5, wide funnel-form, diurnal, inodorous, light purplish-pink with a pinkish brown midstripe and paler margins. Stigmas are green (dull orange in M. pseudoalamensis)Blooming season: Spring, and flowers remain open for about three or four days.Fruits: Berry-like, club shaped, pale scarlet about 20-25 mm long.Seeds: Black, round, finely dotted..Taxonomy notes.Mammillaria pseudoalamensis crops up in commercial listings now and again, but almost invariably turns out to be Mammillaria sheldonii, with a greater radial spines count then Craig called for it M. alamensis ( 9 ) and usually more than the one central described. Reppenhagean favours the name, bur without justifying it in any way. It also surfaced under a Lau collection number (LAU 1401) and it remains to be seen if once again we have a M. sheldonii. If the required spine-count were found in plants resulting from these collections, we would still have merely an extension to the range of variability of M. sheldonii or even Mammillaria mazatlanensis.

Subspecies, varieties, forms and cultivars of plants belonging to the Mammillaria grahamii/sheldonii group

Cultivation and Propagation: Mammillaria alamensis is an easy species in cultivation, recommended for any collection that needs lots of light with ample airflow.Growth rate: It is a small growing, but easily flowering species. It takes several years to offset, but once it starts it can fill a 25 cm pot in just a few years given the best conditions. Soils: It likes very porous standard cactus mix soil with little organic matter (peat, humus). Repotting: Repotting every 2-3 years. It will need a pot with sufficient depth to allow the tap root. As it is especially prone to rot under-pot in a smaller container filled with very porous compost. Use pot with good drainage.Watering: Water regularly in summer, but do not overwater (very wet-sensitively, especially in light of its succulent root system). Its roots are easily lost in pots that stay damp for any length of time. Keep dry with ample airflow in winter. In the rest period no high atmospheric humidity!! Care must be taken with watering as they tends to become swollen and untidy in growth habit if given too much water and shade.Fertilization: During the growing season enrich the soil using a fertilizer rich in potassium and phosphorous, but poor in nitrogen, because this chemical element doesn’t help the development of succulent plants, making them too soft and full of water.Hardiness: Reputedly sensitive to frost , but less so if kept on the dry side prior to, and during, cold weather (hardy to -5° C for short periods, but some reports give it hardy to -12°C). However some warmth throughout the year will increase the grower's success (minimum 5° to 8°C during rest season). Exposition: Outside bright sun, filtered sunlight or afternoon shade, inside it needs bright light, and some direct sun. Subject to sunburn if exposed to direct sun for too long. Tends to bronze in strong light, which encourages flowering and heavy wool and spine production. Uses: It is an excellent plant for container growing. It always looks good and stays small. It look fine in a cold greenhouse and frame.Pests & diseases: It may be attractive to a variety of insects, but plants in good condition should be nearly pest-free, particularly if they are grown in a mineral potting-mix, with good exposure and ventilation. Nonetheless, there are several pests to watch for: - Red spiders: Sensitive to red spider mite. Overhead watering is helpful in controlling mites. - Mealy bugs: Occasionally mealy bugs they develop aerial into the new growth among the wool with disfiguring results, but the worst types develop underground on the roots and are invisible except by their effects. - Scales: Scales are rarely a problem. - Rot: Rot it is only a minor problem with cacti if the plants are watered and “aired” correctly. If they are not, fungicides won't help all that much.Propagation: Direct sow after last frost or (rarely) cuttings. Seeds germinate in 7-14 days at 21-27° C in spring, remove the glass cover gradually as the plants develops and keep ventilated, no full sun for young plants! The seedlings should not be disturbed until they are well rooted, after which they can be planted separately in small pots. Cuttings: wait until the offsets that appear at the base of old clustered specimens are 1/3 the size of the parent and then detach and plant. Cuttings will take root in a minimum temperature of 20° C (but better in hot weather). Cuttings of healthy shoots can be taken in the spring and summer. Cut the stem with a sharp, sterile knife, leave the cutting in a warm, dry place for a week or weeks (depending on how thick the cutting is) until a callus forms over the wound. Once the callus forms, the cutting may be inserted in a container filled with firmed cactus potting mix topped with a surface layer of coarse grit. They should be placed in the coarse grit only; this prevents the cut end from becoming too wet and allows the roots to penetrate the rich compost underneath. The cuttings should root in 2 to 6 weeks.